This invention relates to a door latch for an electrical equipment enclosure. In particular, this invention relates to a flexible door latch which can prevent the door of an electrical equipment enclosure from being forced open during a short circuit overcurrent condition without requiring bolts within the latch.
Electrical equipment enclosures such as those containing, for example, a motor starter, electric switch and a circuit breaker, require durable latches to prevent the enclosure door from blowing open under the arc gas pressure generated upon occurrence of a short-circuit overcurrent condition within any of the enclosed electric equipment. Such latches are often cumbersome due to the mechanical structure needed to withstand the explosive forces generated by the arc pressure on the enclosure door such that some time is required to unlatch the door during routine mechanical maintenance of the enclosed equipment.
One example of a door latch containing a pawl member bolted to a rotatable member is described within U.S. Pat. No. 5,927,766 entitled xe2x80x9cLatching Mechanism for a Motor Control Center.xe2x80x9d
It would be advantageous to provide a pair of compact latches to the door of a motor control center to allow a controlled outwards expansion of the door during intense short-circuit overcurrent conditions to allow arc pressure gas venting while maintaining the door in a virtually closed condition. However, the cumbersome prior door latches have made providing such a pair of latches on a single door significantly expensive in material, time, and labor.
In an exemplary embodiment of the invention, a door latch for latching a door of an electrical equipment enclosure includes a latch body and a latch rod rotatable between locked and unlocked conditions. The latch rod includes a stem with a first end rotatably coupled to the latch body, an extension rod with a first end coupled to a second end of the stem, and a hook coupled to a second end of the extension rod. The extension rod is dimensioned to contact a portion of the electrical equipment enclosure when the latch rod is in the locked condition. The hook is separated form the portion of the electrical equipment enclosure by a clearance distance xe2x80x9cxxe2x80x9d during a quiescent condition within the electrical enclosure. The hook contacts the portion of the electrical equipment enclosure during a pressurized condition within the electrical equipment enclosure. The clearance distance xe2x80x9cxxe2x80x9d is selected to provide a clearance distance xe2x80x9cyxe2x80x9d between the door and the enclosure to allow pressurized gas to escape the enclosure during the pressurized condition.